Constructions for zero-heat-flux, deep tissue temperature measurement devices

ABSTRACT

The invention pertains to flexible devices used for zero-heat-flux, deep tissue temperature measurement, especially to disposable temperature measurement devices. Such a device is constituted of a flexible substrate. An electrical circuit is disposed on a side of the substrate. The electrical circuit includes first and second thermal sensors disposed, respectively, on first and second substrate layers. A heater trace is disposed on the first substrate layer with the first thermal sensor. The first and second substrate layers are separated by a flexible layer of insulation disposed between the first and second substrate layers. The heater trace defines a heater with a central portion that operates with a first power density and a peripheral portion around the central portion that operates with a second power density greater than the first power density.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.12/798,670, filed Apr. 7, 2010.

RELATED APPLICATIONS

This application contains material related to the following US patentapplications:

-   U.S. patent application Ser. No. 12/584,108, filed Aug. 31, 2009,    now U.S. Pat. No. 8,226,294; and,-   U.S. patent application Ser. No. 12/798,668, filed Apr. 7, 2012.

BACKGROUND

The subject matter relates to a temperature device for use in theestimation of deep tissue temperature (DTT) as an indication of the corebody temperature of humans or animals. More particularly, the subjectmatter relates to constructions of zero-heat-flux DTT measurementdevices.

Deep tissue temperature measurement is an estimate of the temperature oforgans that occupy cavities of human and animal bodies (core bodytemperature). DTT measurement is desirable for many reasons. Forexample, maintenance of core body temperature in a normothermic rangeduring the perioperative cycle has been shown to reduce the incidence ofsurgical site infection; and so it is beneficial to monitor a patient'score body temperature before, during, and after surgery. Of coursenoninvasive measurement is highly desirable, for the safety and thecomfort of a patient, and for the convenience of the clinician. Thus, itis most advantageous to obtain a noninvasive DTT measurement by way of adevice placed on the skin.

Noninvasive measurement of DTT by means of a zero-heat-flux device wasdescribed by Fox and Solman in 1971 (Fox R H, Solman A J. A newtechnique for monitoring the deep body temperature in man from theintact skin surface. J. Physiol. January 1971:212(2): pp 8-10). TheFox/Solman system, illustrated in FIG. 1, estimates core bodytemperature using a temperature measurement device 10 with a controlledheater of essentially planar construction that stops or blocks heat flowthrough a portion of the skin. Because the measurement depends on theabsence of heat flux through the skin area where measurement takesplace, the technique is referred to as a “zero heat flux” (ZHF)measurement. Togawa improved the Fox/Solman technique with a DTTmeasurement device structure that accounted for multidimensional heatflow in tissue. (Togawa T. Non-Invasive Deep Body TemperatureMeasurement. In: Rolfe P (ed) Non-Invasive Physiological Measurements.Vol. 1. 1979. Academic Press, London, pp. 261-277). The Togawa device,illustrated in FIG. 2, encloses Fox and Solman's ZHF design in a thickaluminum housing with a cylindrical annulus construction that maintainsradial temperature uniformity in the face of nonuniform radial heatflow.

The Fox/Solman and Togawa devices utilize heat flux normal to the bodyto control the operation of a heater that blocks heat flow from the skinthrough a thermal resistance in order to achieve a desired ZHFcondition. This results in a construction that stacks the heater,thermal resistance, and thermal sensors of a ZHF temperature measurementdevice, which can result in a substantial vertical profile. The thermalmass added by Togawa's cover improves the tissue temperature uniformityof the Fox/Solman design and makes the measurement of deep tissuetemperature more accurate. In this regard, since the goal is zero heatflux through the device, the more thermal resistance the better becauseit increases probe sensitivity. However, the additional thermalresistance adds mass and size, and also increases the time required toreach a stable temperature.

The size, mass, and cost of the Fox/Solman and Togawa devices do notpromote disposability. Consequently, they must be sanitized after use,which exposes them to wear and tear and undetectable damage. The devicesmust also be stored for reuse. As a result, use of these devices raisesthe costs associated with zero-heat-flux DTT measurement and can pose asignificant risk of cross contamination between patients. It is thusdesirable to reduce the size and mass of a zero-heat-flux DTTmeasurement device, without compromising its performance, in order topromote disposability after a single use.

An inexpensive, disposable, zero-heat-flux DTT measurement device isdescribed and claimed in the priority application and illustrated inFIGS. 3 and 4. The device is constituted of a flexible substrate and anelectrical circuit disposed on a surface of the flexible substrate. Theelectrical circuit includes an essentially planar heater which isdefined by an electrically conductive copper trace and which surrounds azone of the surface that is not powered by the heater, a first thermalsensor disposed in the zone, a second thermal sensor disposed outside ofthe heater trace, a plurality of electrical pads disposed outside of theheater trace, and a plurality of conductive traces connecting the firstand second thermal sensors and the heater trace with the plurality ofelectrical pads. Of course, the flexibility of the substrate permits themeasurement device, including the heater, to conform to contours of thebody where measurement is made. Sections of the flexible substrate arefolded together to place the first and second thermal sensors inproximity to each other. A layer of insulation disposed between thesections separates the first and second thermal sensors. The device isoriented for operation so as to position the heater and the firstthermal sensor on one side of the layer of insulation and the secondthermal sensor on the other and in close proximity to an area of skinwhere a measurement is to be taken. As seen in FIG. 4, the layout of theelectrical circuit on a surface of the flexible substrate provides alow-profile, zero-heat-flux DTT measurement device that is essentiallyplanar, even when the sections are folded together. Of course, theflexibility of the substrate permits the measurement device, includingthe heater, to conform to contours of the body where measurement ismade.

Operation of the heater of a zero-heat-flux DTT measurement devicecauses formation of an isothermal channel into tissue under the area ofcontact between the device and the skin of a subject. The zero-heat-fluxDTT measurement is made by way of this isothermal channel. The largerthe area of the heater, the larger the isothermal channel and the moredeeply it penetrates into the tissue. The isothermal channel generallyis at a higher temperature than the tissue which surrounds it, and soheat in the isothermal channel is lost to the surrounding tissue. Thisloss of heat reduces the size and depth of the isothermal channel.

Design and manufacturing choices made with respect to a zero-heat-fluxDTT measurement device can influence the formation of an isothermalchannel. Two such design choices relate to heater construction andmeasurement device size. In this regard, an important measure of heaterperformance is power density, the amount of power (in watts, forexample) that a heater produces per unit of area (in square centimetersor cm², for example). A convenient expression of power density iswatts/cm².

In a zero-heat-flux DTT measurement device, a heater with uniform powerdensity does not generate a uniform temperature across its heat-emittingsurface when the device is in contact with a semi-infinite solid, suchas tissue. For example, if the circularly-shaped heater in themeasurement device of FIG. 3 is invested with uniform power density in aradial direction, the temperature level drops along a radius of theheater in the direction of the periphery when the device is placed onskin. In other words, the heater is cooler near and up to its outer edgethan near its center, and the isothermal channel through which core bodytemperature is measured is narrower than it would be if a uniformtemperature were maintained in the radial direction. Consequently,presuming uniform power density, a progressively larger heater, and thusa larger measurement device, is needed to obtain reasonably accuratedeep tissue readings when the measurement location moves from theforehead, to the neck, to the sternum. For example, a measurement deviceaccording to FIGS. 3 and 4 with a uniform density heater needs a firstminimum diameter, for example about 30 mm (707 mm²), to accuratelymeasure core body temperature at the forehead. However, such auniform-power-density measurement device needs a second, larger, minimumdiameter, for example about 40 mm (1257 mm²), for reasonable measurementaccuracy on the neck. We have found that a uniform-power-densitymeasurement device with a third minimum diameter, for example about 50mm (1963 mm²), is too small to obtain reasonable accuracy through thesternum. We also note that Fox and Solman used a 60 mm square (3600 mm²)zero-heat-flux DTT measurement device with a uniform power density formeasurement through the sternum.

However, a zero-heat-flux DTT measurement device fabricated in a singlesize with a uniform-power-density heater that meets performancerequirements for the deepest core body temperature measurement might betoo large to be used at other measurement sites. Depending on thelocation, space for taking a core body measurement can be limited,especially if other measurements are made nearby. For example, abdominalor thoracic surgery might require simultaneous measurement of brainactivity, blood oxygen, and core body temperature. In such a case, anoptimal measurement site for placement of BIS electrodes, an oxygenmonitor, and a DTT measurement device would be on the patient's head;preferably the patient's forehead (including the temples) which isconvenient to use, nonsterile, visible, and validated for measuring corebody temperature. Manifestly, the forehead area available for placementof measurement devices can quickly become limited as the number ofdifferent measurements increases. Accordingly, constructions for adisposable, noninvasive, zero-heat-flux DTT measurement device shouldhave a relatively small contact area. However, downward scaling of auniform-power-density device can reduce the reliability of thetemperature measurements produced by a smaller device for at least tworeasons: deterioration of the isothermal channel through which DTT ismeasured and influence of nonpowered areas on temperature uniformity.

Generally, zero-heat-flux DTT measurement requires a heater with thecapacity to deliver enough heat to create and maintain an isothermalchannel to some required depth. Reduction of the size of the measurementdevice requires constructions that still deliver enough heat to createthe isothermal channel and that do not compromise the uniformity withwhich the heat is delivered. However, as the size of the heater isreduced, the size and depth of the isothermal channel is reduced, makingit more susceptible to being compromised by the effects ofmultidimensional heat loss in surrounding tissue. This effect can bemore pronounced at measurement sites where the core temperature isrelatively deep in the body, such as on the sternum.

Reduction of heater size can also increase the effect which nonpoweredareas of the measurement device have on the temperature uniformity ofthe heater. For a measurement device fabricated by metal depositiontechniques, the conductive traces for thermal sensors and otherelectronic elements deliver no heat and occupy areas which are notpowered by the heater. In some designs, such unpowered areas penetratethe heater, thereby reducing the temperature uniformity of themeasurement device.

Inconsistencies and irregularities in the thermal insulation near thefirst thermal sensor can influence its operation and cause it to producefaulty readings. As the size of the measurement device is reduced, theseinconsistencies and irregularities increasingly compromise theuniformity of the temperature.

Finally, if additional electronic elements are added to a zero-heat-fluxDTT measurement device, additional leads and connections must beprovided, which increases the total nonpowered area of the device andadditionally complicates the heater layout.

SUMMARY

An object of an invention completed in respect of the problems describedabove is to reduce the influence of multidimensional heat flow in tissueon the operation of a zero-heat-flux DTT measurement device constitutedof a flexible substrate and an electrical circuit including a heaterdefined by a conductive trace which is disposed on a surface of theflexible substrate.

Another object of an invention completed in respect of the problemsdescribed above is to reduce the size of a zero-heat-flux DTTmeasurement device constituted of a flexible substrate and an electricalcircuit including a heater defined by a conductive trace which isdisposed on a surface of the flexible substrate, without compromisingthe ability of the device in creating an isothermal channel by whichcore body temperature is measured.

Another object of an invention completed in respect of the problemsdescribed above is to reduce the size of a zero-heat-flux DTTmeasurement device constituted of a flexible substrate and an electricalcircuit including a heater defined by a conductive trace which isdisposed on a surface of the flexible substrate, without compromisingthe uniformity of the temperature generated by the device to create anisothermal zone by which deep tissue temperature is measured.

Another object of an invention completed in respect of the problemsdescribed above is to reduce the size of a zero-heat-flux DTTmeasurement device constituted of a flexible substrate and electricallyconductive traces on a surface of the substrate for a heater, at leasttwo thermal sensors, and at least one additional electronic device.

These and other objects are achieved with a zero-heat-flux DTTmeasurement device constituted of a flexible substrate and an electricalcircuit including a heater trace defining a generally planar heatersurrounding a zone on a surface of the substrate, in which the heaterhas a central power density portion and a peripheral power densityportion surrounding the central power density portion.

Preferably, the heater trace defines a heater with a central portionthat surrounds the zone and has a first power density and a peripheralportion that surrounds the central portion and has a second powerdensity that is greater than the first power density.

Alternatively, the heater trace defines a heater with a central heaterelement that surrounds the zone and a peripheral heater element aroundthe outer periphery of the central heater element, in which the centraland peripheral heater elements are separately controllable.

These and other objects are achieved with a zero-heat-flux DTTmeasurement device constituted of a flexible substrate and an electricalcircuit including a heater trace with a pattern defining an annularheater, in which the heater trace has a power density with a first valuein an area where the pattern is uninterrupted and a second value inareas where the pattern is interrupted, wherein the second value isgreater than the first value.

These and other objects are achieved with a zero-heat-flux DTTmeasurement device constituted of a flexible substrate including acenter section, a tab extending outwardly from the periphery of thecenter section, a tail extending outwardly from the periphery of thecenter section, and an electrical circuit on a surface of the flexiblesubstrate, the electrical circuit including a heater trace defining aheater surrounding a zone of the surface, a first thermal sensordisposed in the zone, a second thermal sensor disposed on the tail, aplurality of electrical pads disposed on the tab, and a plurality ofconductive traces connecting the first and second thermal sensors andthe heater trace with the plurality of electrical pads, in which thetail and tab are separated so as to provide a path on the surface forthe conductive traces connecting the second thermal sensor withelectrical pads which is easily routed and does not cross the heatertrace.

These and other objects are achieved with a zero-heat-flux DTTmeasurement device constituted of a flexible substrate and an electricalcircuit on a surface of the flexible substrate, the electrical circuitincluding a heater trace defining a heater surrounding a zone of thesurface, a first thermal sensor disposed in the zone, a second thermalsensor disposed outside of the heater, a plurality of electrical pads,and a plurality of conductive traces connecting the first and secondthermal sensors and the heater trace with the plurality of electricalpads, in which at least one of the conductive traces is shared by atleast two elements of the electrical circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a first prior art deep tissuetemperature measurement system including a ZHF DTT measurement device.

FIG. 2 is a schematic side sectional diagram of a second prior art deeptissue temperature measurement system including a ZHF deep tissuetemperature measurement device with an aluminum cap.

FIG. 3 is a plan view of a side of a flexible substrate showing anelectrical circuit disposed on a surface of the substrate fortemperature measurement.

FIG. 4 is a side sectional view of a temperature device thatincorporates the electrical circuit of FIG. 3.

FIG. 5 is an exploded assembly view, in perspective, showing elements ofthe temperature device of FIG. 4.

FIGS. 6A-6F illustrate a method of temperature device manufacture basedon the temperature device of FIGS. 4 and 5.

FIG. 7 is a side sectional, partly schematic illustration of azero-heat-flux DTT measurement device with a heater having central andperipheral portions.

FIG. 8A illustrates a first construction of the zero-heat-flux DTTmeasurement device construction of FIG. 7, and FIG. 8B is a schematicdiagram including elements of the measurement device.

FIG. 9 is a block diagram illustrating a temperature measurement systemincluding a zero-heat-flux DTT measurement device.

FIG. 10 illustrates a second construction of the zero-heat-flux DTTmeasurement device construction of FIG. 7.

FIG. 11 illustrates a third construction of the zero-heat-flux DTTmeasurement device construction of FIG. 7.

FIG. 12 illustrates a fourth construction of the zero-heat-flux DTTmeasurement device construction of FIG. 7.

FIG. 13 illustrates a fifth construction of the zero-heat-flux DTTmeasurement device construction of FIG. 7.

FIG. 14 illustrates a sixth construction of the zero-heat-flux DTTmeasurement device construction of FIG. 7.

FIG. 15 illustrates a seventh construction of the zero-heat-flux DTTmeasurement device construction of FIG. 7.

FIG. 16 illustrates an eighth construction of the zero-heat-flux DTTmeasurement device construction of FIG. 7.

FIG. 17 illustrates a ninth construction of the zero-heat-flux DTTmeasurement device construction of FIG. 7.

FIG. 18 illustrates a tenth construction of the zero-heat-flux DTTmeasurement device construction of FIG. 7

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

It is desirable that zero heat flux, deep tissue temperature measurementdevice constructions contact a minimal area of skin when placed for use,while creating and maintaining a well-formed isothermal channel forreliable, accurate measurement of core body temperature. Theconstructions should have a low mass and a low profile, and shouldpresent a relatively small area which contacts skin in order to make themeasurement (hereinafter, this area is referred to as the “contact area”of the device). It is particularly desirable that a low-profile, lightweight, flexible DTT measurement device construction enable zero heatflux temperature measurement at more than one site on a human or animalbody.

A temperature device for zero-heat-flux DTT measurement includes aflexible substrate with at least two thermal sensors disposed in aspaced-apart relationship and separated by one or more flexible layersof thermally insulating material. Preferably the sensors are maintainedin a spaced apart relationship by a flexible thermal (and electrical)insulator. The substrate supports at least the thermal sensors, theseparating thermal insulator, and a heater. It is desirable that thesubstrate also support at least one additional electronic device inorder to enrich the functionality of the temperature device.

Although temperature device constructions are described in terms ofpreferred embodiments comprising representative elements, theembodiments are merely illustrative. It is possible that otherembodiments will include more elements, or fewer, than described. It isalso possible that some of the described elements will be deleted,and/or other elements that are not described will be added. Further,elements may be combined with other elements, and/or partitioned intoadditional elements.

A Zero-Heat-Flux DTT Measurement Device

A layout for a zero-heat-flux, DTT measurement device is illustrated inFIG. 3. The device includes an electrical circuit disposed on a flexiblesubstrate in order to adapt or conform the physical configuration of thetemperature measurement device to differing contours encountered atdifferent temperature measurement locations. Preferably, but notnecessarily, the flexible substrate is constructed or fabricated to havea plurality of contiguous sections. For example, the flexible substrate100 has three contiguous sections 102, 104, and 106. The first, orcenter, section 102 is substantially circular in shape. The secondsection (or “tail”) 104 has the shape of a narrow, elongate rectanglethat extends in a first radial direction from the periphery of the firstsection 102. Where the center section and the tail join at 105, theperiphery of the center section has a straight portion and the width ofthe tail is reduced. The third, or tab, section 106 has the shape of abroad, elongate rectangle that extends in a second radial direction fromthe periphery of the center section 102. Preferably, the tail and tabare aligned along a diameter of the center section.

As per FIG. 3, the elements of the electronic circuit are disposed on asingle surface, on a first side 108 of the flexible substrate. A firstthermal sensor 120 is positioned inside the outer perimeter of thecenter section 102, preferably near or at the center of the centersection 102. An electrically conductive heater trace 122 defines aheater with a shape that surrounds or encircles a zone 121 in which thefirst thermal sensor 120 is located. In the preferred embodimentillustrated in FIG. 3, the heater trace has an annular shape thatincludes a circular array of wedge-shaped heater zones 124 that surroundor encircle the zone 121 and the first thermal sensor 120 which isdisposed in the zone. A second thermal sensor 126 is positioned on thetail 104. A plurality of electrical connection pads 130 is located onthe tab 106. The heater trace includes two electrically conductive tracesections that terminate in the connection pads 130 a and 130 b. Twoelectrically conductive traces extend between mounting pads on which thefirst thermal sensor 120 is mounted and the connection pads 130 c and130 d. Two additional electrically conductive traces extend betweenmounting pads on which the second thermal sensor 126 is mounted and theconnection pads 130 e and 130 f.

In the specific layout shown of the preferred embodiment shown in FIG.3, the path of the heater trace 122 crosses the paths of the two tracesfor the second thermal sensor 126. In this case, the continuity of theheater trace is preferably, but not necessarily, maintained by anelectrically conductive zero-ohm jumper 132 which crosses, and iselectrically isolated from, the two traces for the second thermal sensor126. In other embodiments, the continuity of the heater trace 122 canalso be maintained by vias to the second side of the flexible substrate,by running the thermal sensor traces around the periphery of the firstside of the flexible substrate, by a jumper wire instead of the zero-ohmresistor, or by any equivalent solution.

The flexibility or conformability of the flexible substrate can beenhanced by a plurality of slits 133 that define zones which move orflex independently of each other. In the preferred embodiment, the slits133 are made in the center section 102 in a pattern that follows oraccommodates the layout of the heater trace 122. The pattern at leastpartially separates the heater zones 124 so as to allow any one of theheater zones 124 to move independently of any other heater zone. Thepreferred pattern of slits is a radial pattern in that each slit is madealong a respective radius of the circular center section 102, betweenadjacent heater zones, and extends along the radius from the peripheryof the center section 102 toward the center of the circular shape of thesection. This is not meant to exclude other possible slit configurationsdetermined by the different shapes of the heater trace layout and theflexible substrate sections.

Sections of the flexible substrate are brought or folded together aboutan insulator to provide thermal resistance between the first and secondthermal sensors 120 and 126 in a configuration that is preferred for ZHFtemperature measurement. For example, at least the center and tailsections 102 and 104 of the flexible substrate are brought or foldedtogether about a flexible insulator. Preferably, the first and secondthermal sensors 120 and 126 are thereby disposed on respective sides ofa thermal insulator. In this regard, with reference to FIGS. 3 and 4,the center section 102 and tail 104 are folded together about a flexiblelayer of insulating material 140. The layer 140 provides thermal andelectrical resistance between the thermal sensors; it also supports thethermal sensors in a spaced-apart configuration.

A flexible temperature measurement device construction includes anelectrical circuit laid out on a side of a flexible substrate as shownin FIG. 3. With two sections of the flexible substrate brought or foldedtogether so as to sandwich a flexible insulator, the construction has amultilayer structure as best seen in FIG. 4. Thus, a temperaturemeasurement device 200 includes the electrical circuit laid out on thesurface of the first side 108 of the flexible substrate 100. The centraland tail sections 102 and 104 are brought or folded together about theflexible insulating layer 140 so as to provide a thermal resistancebetween the first and second thermal sensors 120 and 126. The flexibleinsulating layer also maintains the first and second thermal sensorsdisposed in a spaced relationship. Preferably, but not necessarily, thesecond thermal sensor 126 is aligned with the first thermal sensor on aline 202 which passes through the zone 121 that is surrounded by theheater trace (seen in FIG. 3). The temperature measurement devicefurther includes a flexible heater insulator 208 attached to a secondside 109 of the substrate 100, over the center section 102.

The layout of the electrical circuit illustrated in FIG. 3 locates allof the circuit components on a single surface on one side of theflexible substrate 100. This layout confers several advantages. First,it requires only a single fabrication sequence to lay down traces forthe heater, the thermal sensors, and the connection pads, therebysimplifying manufacture of the device. Second, when the sectionscarrying the thermal sensors are folded together, the thermal sensorsare maintained within a thermally and mechanically controlledenvironment.

Another benefit of the preferred layout shown in FIG. 3 is that thefirst thermal sensor 120 is physically separated from the heater, in azone 121 that is surrounded or encircled by the heater trace 122, andnot stacked under it as in the Fox/Solman system. When the temperaturemeasurement device is activated, the heater is turned on and the heatproduced thereby travels generally vertically from the heater to thepatient, but only medially to the first thermal sensor. As a result, thejump in temperature that occurs when the heater is activated is notimmediately sensed by the first thermal sensor, which improves controlof the heater and stability of the temperature measurement withoutrequiring an increase in thermal mass of the temperature measurementdevice. Thus, the first temperature sensor 120 is preferably located inthe same plane, or on the same surface, as the heater trace 122 (and caneven be elevated slightly above the heater trace), and substantially inor in alignment with the zone 121 of zero heat flux.

It is desirable that the temperature measurement device support apluggable interface for convenience and for modularity of a patientvital signs monitoring system. In this regard, and with reference toFIGS. 3 and 4, the tab 106 is configured with the array of pads 130 soas to be able to slide into and out of connection with a connector (notshown). In order to provide a physically robust structure capable ofmaintaining its shape while being connected and disconnected, the tab106 is optionally stiffened. In this regard, a flexible stiffener 204 isdisposed on the second side 109 of the flexible substrate 100. Thestiffener extends substantially coextensively with the tab 106 and atleast partially over the center section 102. As best seen in FIG. 4, thestiffener 204 is disposed between the second side 109 of the flexiblesubstrate 100 and the flexible insulator 208. A key to align the tab 106and prevent misconnection with an electrical connector (not shown) andto retain the connector on the tab may be provided on the device 200.For example, with reference to FIG. 5, such a key includes an opening209 through the stiffener and tab.

The temperature measurement device 200 is mounted on a region of skinwhere temperature is to be measured with the second thermal sensor 126closest to the skin. As seen in FIG. 4, a layer of adhesive 222 isdisposed on the second side 109, on the layer of insulation 140 and theportion of the tail 104 where the second sensor 126 is located. Arelease liner (not shown in this figure) may be peeled from the layer ofadhesive 222 to prepare the device 200 for attachment to the skin. Whendeployed as shown in FIG. 4, a pluggable signal interface between theelectrical circuit on the device 200 and a temperature measurementsystem is provided through the plurality of electrical connection pads130 located in the tab 106. The signals transferred therethrough wouldinclude at least heater activation and thermal sensor signals.

Use of an electrical circuit on a flexible substrate greatly simplifiesthe construction of a disposable temperature device for estimating deeptissue temperature, and substantially reduces the time and cost ofmanufacturing such a device. In this regard, manufacture of atemperature measurement device incorporating an electrical circuit laidout on a side of the flexible substrate 100 with the circuit elementsillustrated in FIG. 3 may be understood with reference to FIGS. 5 and6A-6F. Although a manufacturing method is described in terms ofspecifically numbered steps, it is possible to vary the sequence of thesteps while achieving the same result. For various reasons, some of thesteps may include more operations, or fewer, than described. For thesame or additional reasons, some of the described steps may be deleted,and/or other steps that are not described may be added. Further, stepsmay be combined with other steps, and/or partitioned into additionalsteps.

In FIG. 6A, the traces and pads for an electrical circuit are fabricatedon a first side 108 of a flexible substrate 100 with a center section102, a tail 104 extending from the center section, and a tab 106extending from the center section. The electronic elements (first andsecond thermal sensors) are mounted to the traces to complete anelectrical circuit (which is omitted from these figures for convenience)including the elements of FIG. 3, laid out as shown in that figure. Ifused, the pattern of slits 133 separating the heater zones may be madein the center section in this manufacturing step.

As per FIG. 6B, in a second manufacturing step, a stiffener 204 islaminated to a second side of the flexible substrate. As best seen inFIG. 5, the stiffener has a portion shaped identically to the tab andnarrows to an elongated portion with a circular tip. When laminated tothe second side 109, the stiffener substantially extends over the taband partially over the center section, beneath the zone 121. Preferably,an adhesive film (not seen), or equivalent, attaches the stiffener tothe second side of the flexible substrate.

As per FIG. 6C, in a third manufacturing step, a flexible layer 208 ofinsulating material is attached by adhesive or equivalent to the firstside of the flexible substrate, over substantially all of the centersection and at least a portion of the stiffener. This layer is providedto insulate the heater from the ambient environment. As best seen inFIG. 5, this flexible layer may include a truncated tab 210 thatprovides additional reinforcement to a pluggable connection between thetab 106 and a system connector.

As per FIG. 6D, in a fourth manufacturing step, a flexible central layerof insulating material 140 is attached to the first side 108, over thecenter section, to cover the heater trace and the first thermal sensor.As best seen in FIG. 5, this flexible layer may also include a truncatedtab 141 that provides additional reinforcement to a pluggable connectionbetween the tab and a system connector.

As per FIG. 6E, in a fifth manufacturing step, the tail 104 is foldedover the central layer of insulating material 140 such that the firstand second thermal sensors are maintained by the central layer in thepreferred spaced relationship.

As per FIG. 6F, in a sixth manufacturing step, a layer of adhesive (notseen) with a release liner 226 is attached to the central insulatinglayer, over the central insulating layer with the tail folded thereto.As best seen in FIG. 5, the release liner 226 may have a shape thatcorresponds to the central section 102 and tab 106.

In a best mode of practice, a temperature measurement device accordingto this specification has been fabricated using the materials and partslisted in the following table. An electrical circuit with copper tracesand pads conforming to FIG. 3 was formed on a flexible substrate ofpolyimide film by a conventional photo-etching technique and thermalsensors were mounted using a conventional surface mount technique. Thedimensions in the table are thicknesses, except that Ø signifiesdiameter. Of course, these materials and dimensions are onlyillustrative and in no way limit the scope of this specification. Forexample, traces may be made wholly or partly with electricallyconductive ink.

Table of Materials and Parts: I Representative Element Materialdimensions Flexible Kapton ® polyimide film with Substrate 100: 0.05 mmsubstrate deposited and photo-etched copper traces and pads Thermal NTCthermistors, Part # R603- sensors 103F-3435-C, Redfish Sensors FlexibleClosed cell polyethylene foam Insulator 208: insulating with skinnedmajor surfaces Ø50 × 1.5 mm layers coated with pressure sensitiveInsulator 140: adhesive (PSA) Ø50 × 3.0 mm Stiffener Polyethyleneterephthalate Stiffener 204: 0.25 mm (PET)Zero-Heat-Flux DTT Measurement Device Constructions

Zero-heat-flux DTT measurement devices according to FIG. 3 and thepreceding description have been fabricated, assembled, and clinicallytested. We have found that it is desirable to further adapt theconstruction of such devices so as to increase the number of sites wherethey can be deployed, without necessarily enlarging the devices orsacrificing the accuracy with which they perform DTT measurement.

These objectives are met by a heater construction with a central powerdensity portion and a peripheral power density, portion surrounding thecentral power density portion. The central power density portionoperates with a first power density and the peripheral power densityportion operates with a second power density of a higher magnitude thanthe first power density so as to maintain a substantially uniformtemperature from the central heater portion to the periphery of theheater when the device is placed on skin to measure core bodytemperature.

FIG. 7 is a sectional, partially-schematic illustration of a preferredzero-heat-flux DTT measurement device construction. Not all elements ofthe measurement device are shown in the figure; however, the figure doesshow relationships between components of the construction that arerelevant to zero-heat-flux measurement. The measurement device 700includes flexible substrate layers, a layer of thermally insulatingmaterial, and an electrical circuit. The electrical circuit includes aheater 726, a first thermal sensor 740, and a second thermal sensor 742.The heater 726 and the first thermal sensor 740 are disposed in or on aflexible substrate layer 703 and the second thermal sensor 742 isdisposed in or on a flexible substrate layer 704. The first and secondsubstrate layers 703 and 704 are separated by a flexible layer 702 ofthermally insulating material. The flexible substrate layers 703 and 704can be separate elements, but it is preferred that they be sections of asingle flexible substrate folded around the layer of insulatingmaterial. Preferably, adhesive film (not shown) attaches the substrateto the insulating layer 702. A layer of adhesive material 705 mounted toone side of the substrate layer 704 is provided with a removable liner(not shown) to attach the measurement device to skin. Preferably, aflexible layer 709 of insulating material lies over the layers 702, 703,and 704 and is attached by adhesive film (not shown) to one side of thesubstrate layer 702. The insulating layer 709 extends over the heater726 and the first thermal sensor 740.

In use, the measurement device 700 is disposed with the second thermalsensor 742 nearest the skin. The layer 702 is sandwiched between thefirst and second substrate layers 703 and 704 so as to separate theheater 726 and first thermal sensor 740 from the second thermal sensor742. In operation, the layer 702 acts as a large thermal resistancebetween the first and second thermal sensors, the second thermal sensor742 senses the temperature of the skin, and the first thermal sensorsenses the temperature of the layer 702. While the temperature sensed bythe first thermal sensor 740 is less than the temperature sensed by thesecond thermal sensor 742, the heater is operated to reduce heat flowthrough the layer 702 and the skin. When the temperature of the layer702 equals that of the skin, heat flow through the layer 702 stops andthe heater is switched off. This is the zero-heat-flux condition as itis sensed by the first and second sensors 740 and 742. When thezero-heat-flux condition occurs, the temperature of the skin, indicatedby the second thermal sensor, is interpreted as core body temperature.In the zero-heat-flux DTT measurement device constructions that are tobe described in detail, the heater 726 has a central heater portion 728that operates with a first power density, and a peripheral heaterportion 729 surrounding the central heater portion that operates with asecond power density higher than the first power density. Of course, theflexibility of the substrate permits the measurement device 700,including the heater 726, to conform to body contours where measurementis made.

With reference to FIG. 8A, a first construction of a zero-heat-flux DTTmeasurement device 700 includes a flexible substrate 701. Preferably,but not necessarily, the flexible substrate 701 has contiguous sections705, 706, and 708. Preferably, but not necessarily, the first, orcenter, section 705 is substantially circular in shape. The secondsection (or “tail”) 706 has the shape of a narrow, elongated rectanglewith a bulbous end 707 that extends outwardly from the periphery of thecenter section 705 in a first direction. The third section (or “tab”)708 has the shape of a wide rectangle that extends outwardly from theperiphery of the center section 705 in a second direction. Opposingnotches 710 are formed in the tab 708 to receive and retain respectivespring-loaded retainers of a cable connector (not shown). Preferably butnot necessarily, the tail 706 is displaced from the tab 708 by anarcuate distance of less than or equal to 180° in either a clockwise ora counterclockwise direction.

As per FIG. 8A, an electrical circuit 720 is disposed on the flexiblesubstrate 701. Preferably, but not necessarily, the elements of theelectrical circuit 720 are located on the surface 721 of the flexiblesubstrate 701. The electrical circuit 720 includes at least anelectrically conductive heater trace, thermal sensors, electricallyconductive connective trace portions, and electrical connection pads. Itis desirable that some, but not necessarily all, embodiments of theelectrical circuit 720 also include at least one multi-pin electroniccircuit device, such as an electronically programmable memory 770. Theheater trace 724 defines a generally annular heater 726 surrounding azone 730 of the substrate 701 into which no portion of the heater trace724 extends; in this regard, the zone 730 is not directly heated whenthe heater operates. The zone 730 occupies a generally circular portionof the surface 721. More completely, the zone 730 is a cylindricalsection of the substrate 701 which includes the portion of the surface721 seen in FIG. 8A, the counterpart portion of the opposing surface(not seen in this figure), and the solid portion therebetween.Preferably, but not necessarily, the zone 730 is centered in the centersection 705 and is concentric with the heater 726. A first thermalsensor 740 is mounted on mounting pads formed in the zone 730. A secondthermal sensor 742 is mounted on mounting pads disposed outside of thegenerally annular heater 726; preferably, these mounting pads are formedgenerally near the end of the tail, for example, in or near the centerof the bulbous end 707 of the tail. In some constructions the electricalcircuit 720 includes at least one multi-pin electronic circuit devicemounted on the measurement device 700. For example anelectrically-erasable programmable read/write memory 770, is mounted onmounting pads formed on a portion of the surface 721 on the centersection 705 near or adjacent the tab 708. Electrical connection pads(“electrical pads”) are formed on the surface 721, in the tab 708. Aplurality of conductive trace portions 725 connects the first and secondthermal sensors and the heater trace with a plurality of the electricalpads 771. If the measurement device 700 includes a multi-pin electroniccircuit device, one or more additional electrical pads and additionalconductive trace portions are provided for the device; preferably, butnot necessarily, at least one such additional pad is shared by thedevice and one of the heater, the first thermal sensor, and the secondthermal sensor.

As seen in FIG. 8A, preferably, but not necessarily, the center section705 has formed therein a plurality of slits 751, 752 to enhance theflexibility and conformability of the flexible substrate. The slitsextend radially from the periphery toward the center of the centersection 705. The slits define zones which move or flex independently ofeach other. The layout of the heater trace 724 is adapted to accommodatethe slits. In this regard, the heater trace follows a zigzag orswitchback pattern with legs that increase in length from the peripheryof the zone 730 to the ends of the longer slits 751 and then, after astep decrease at those ends, generally increase in length again to theouter periphery of the heater 726 in the zones defined by the slits. Asillustrated, the construction of the heater has a generally annularshape centered in the zone 730, although the annularity is interruptedby the slits. Alternatively, the annular shape can be viewed asincluding a peripheral annulus of wedge-shaped heater zones surroundinga generally continuous central annulus.

A non-uniform power density heater structure can be understood withreference to FIG. 8A, where the heater 726 includes a central portion728 (indicated by lightly drawn lines) having a first power density anda peripheral portion 729 (indicated by heavily drawn lines) whichsurrounds the central portion 728 and has a second power density higherthan the first power density. The heater trace 724 is continuous andincludes two ends, a first of which transitions to electrical pad 5, andthe second to electrical pad 6. However, because of the slits, each ofthe central and peripheral portions 728 and 729 includes a plurality ofsections arranged in a sequence, in which the sections of the centralportion 728 alternate with the sections of the peripheral portion.Nevertheless, the annular structure of the heater arrays the sections ofthe central portion 728 generally in a central annulus around the zone730, and arrays the sections of the peripheral portion 729 around thecentral portion 728. When the heater 726 is operated, the centralportion 728 produces a central annulus of heat at the first powerdensity surrounding the zone 730 and the peripheral portion 729 producesa ring-shaped annulus of heat at the second power density that surroundsthe central annulus of heat.

Preferably the heater trace 724 is continuous, but exhibits a nonuniformpower density along its length such that the central heater portion 728has a first power density and the peripheral portion 729 has a secondpower density that is greater than the first power density. With thisconfiguration, a driving voltage applied to the heater 726 will causethe central heater portion 728 to produce less power per unit of heaterarea of the heater trace than the outer heater portion 729. The resultwill be a central annulus of heat at a first average power surrounded bya ring of heat a second average power higher than the first.

The differing power densities of the heater portions 728 and 729 may beinvariant within each portion, or they may vary. Variation of powerdensity may be step-wise or continuous. Power density is most simply andeconomically established by the width of the heater trace 724 and/or thepitch (distance) between the legs of a switchback pattern. For example,the resistance, and therefore the power generated by the heater trace,varies inversely with the width of the trace. For any resistance, thepower generated by the heater trace also varies inversely with the pitchof (distance between) the switchback legs.

The electrical circuit 720 on the flexible substrate 701 seen in FIG. 8Ais shown in schematic form in FIG. 8B. The electrical pads on the tab708 numbered 1-6 in FIG. 8A correspond to the identically-numberedelements in FIG. 8B. The number of electrical pads shown is merely forillustration. More, or fewer, electrical pads can be used; any specificnumber is determined by design choices including the presence or absenceof a multi-pin electronic device, the heater construction, the number ofthermal sensors, and so on. In some constructions it is desirable toutilize one or more of the electrical pads for electrical signalconduction to or from more than a single element of the electricalcircuit 720 in order to minimize the number of electrical pads, therebysimplifying the circuit layout, minimizing the size and mass of the tab708, and reducing interface connector size.

Presume that the electrical circuit 720 includes a multi-pinelectronically programmable memory (EEPROM) 770 such as a 24AA01T-I/OTmanufactured by Microchip Technology and mounted by mounting pads to thezero-heat-flux DTT measurement device 700. FIGS. 8A and 8B illustrate aconstruction in which one or more electrical pads are shared by at leasttwo elements of the electrical circuit. In this regard:

one lead of the second thermal sensor 742 and pin 1 of the memory 770are connected by conductive trace portions to electrical pad 1;

leads of the first and second thermal sensors 740 and 742 and pin 4 ofthe memory 770 are connected by conductive trace portions to electricalpad 2;

one lead of the first thermal sensor 740 and pin 3 of the memory 770 areconnected by conductive trace portions to electrical pad 3;

pins 2 and 5 of the memory 770 are connected by a conductive traceportion to electrical pad 4;

the return end of the heater trace 724 is connected by a conductivetrace portion to electrical pad 5; and

the input end of the heater trace 724 is connected by a conductive traceportion to electrical pad 6.

With reference to FIGS. 7 and 8A, when the measurement device 700 isassembled, the center section 705 and tail 706 are folded together abouta flexible layer of insulating material such as the layer 702. The layer702 provides thermal resistance and electrical insulation between thethermal sensors; it also supports the thermal sensors in a spaced-apartconfiguration. In other words, the first and second thermal sensors 740and 742 are disposed on respective layers of substrate material that areseparated by the layer of insulating material with the heater and firstthermal sensor facing one side of the layer of insulating material andthe second thermal sensor facing the other.

Refer again to FIG. 8A for an understanding of elements of themeasurement device 700 that maintain or improve the uniformity oftemperature produced by operation of the heater 726. While theseelements do produce desirable effects in temperature uniformity,incorporation of any one or more of these elements into the constructionof a zero-heat-flux DTT measurement device is optional. Nonpowered areaswithin the footprint of the heater 726 can compromise temperatureuniformity enough to destabilize the zero-heat-flux condition importantto making accurate measurements. Accordingly, it is desirable to reduce,if not eliminate, the destabilizing effects of nonpowered areas withinthe footprint of the heater. In this regard, an elongate heater traceportion with a high power density is formed along a flank of each slit,parallel to the slit; see for example the long heater trace portion 774that runs along the flank of and parallel to the long slit 751 and theshort heater trace portion 775 along the flank of and parallel to theshort slit 752. During operation of the heater 726, the high powerdensity of these heater trace portions elevates the power in the areasthat flank the slits to help maintain the temperature uniformity of thedevice. In addition, an elongate heater trace portion 776 with a highpower density of the heater trace 724 runs from electrical pad 6 alongthe aisle 780 where the conductive traces for the first thermal sensor740 extend. During operation of the heater 726, this heater traceportion elevates the power in the aisle 780.

With respect to FIG. 8A, irregular or incomplete insulation of thenonpowered zone 730 can reduce the accuracy with which thezero-heat-flux condition is sensed. In this regard, the center section705 and tail 706 are folded together over a layer of thermal insulationin the manner of FIG. 6D when the measurement device 700 is assembledfor use. Preferably, the end of the tail 706 overlays the zone 730. Ifthe end of the tail presents an irregular or incomplete insulation ofthe zone 730, it is possible that a cold spot can form and compromisethe operation of the first thermal sensor 740, which is positioned inthe zone. Accordingly, the end 707 of the tail 706 has an enlargedbulbous shape that aligns with and overlaps the zone 730, therebymaintaining a regular, continuous level of thermal insulation thatoverlies the zone.

The zero-heat-flux DTT measurement device 700, with the electricalcircuit 720 laid out on one or more sides of the flexible substrate 701as illustrated in FIG. 8A, can be manufactured and assembled in themanner illustrated in FIGS. 5 and 6A-6F, using materials identified inthe Table of Materials and Parts II. Preferably, the measurement deviceis constructed with a flexible stiffener comprising a separate piece ora layer of material painted, deposited, or formed on the tab 708 andthen hardened. Preferably, with reference to FIGS. 4 and 8A, a stiffenerfor the tab 708 (FIG. 8A) is disposed on the side of the flexiblesubstrate 701 that corresponds to the second side 109 of the flexiblesubstrate 100 (FIG. 4). The stiffener extends substantiallycoextensively with the tab 708, and at least partially over the centersection 705, but stops short of the zone 730, approximately whereindicated by the dashed line 711 in FIG. 8A.

The physical layout of FIG. 8A and the corresponding electrical circuitof FIG. 8B illustrate an interface by which operation of azero-heat-flux DTT measurement device can be controlled and monitored ina DTT measurement system. FIG. 9 illustrates a signal interface betweena zero-heat-flux DTT measurement device according to FIG. 7, using thefirst construction of FIG. 8A as an example. With reference to thesefigures, a DTT measurement system includes control mechanization 800, ameasurement device 700, and an interface 785 that transfers power,common, and data signals between the control mechanization and themeasurement device. The interface can be wireless, with transceiverslocated to send and receive signals. Preferably, the interface includesa cable 787 with a connector 789 releasably connected to the tab 708.The control mechanization 800 manages the provision of power and commonsignals on respective signal paths to the heater and provides for theseparation of the signals that share a common signal path, such as theThermistor2 (TH2) and SCL signals. A common reference voltage signal isprovided on a single signal path to the thermal sensors, and respectiveseparate return signal paths provide sensor data from the thermalsensors.

Presuming inclusion of an EEPROM on the measurement device 700, aseparate signal path is provided for EEPROM ground, and the thermalsensor signal paths are shared with various pins of the EEPROM as perFIGS. 8A and 8B. This signal path configuration separates the digitalground for the EEPROM from the DC ground (common) for the heater, forgood reason. Presume that the EEPROM and the heater share an electricalpad for ground. The cable 787 including its connector contacts has acertain amount of resistance. If the heater 726 is powered up, thecurrent through it has to return to the control mechanization 800through the ground (common) contact, which means there will be somevoltage developed on the measurement device side of the contact equal tothe resistance of that line multiplied by the current through the heater726. That voltage could be as high as 2 or 3 volts depending on theintegrity of the contacts. If concurrently the supply voltage goes lowon the EEPROM or even one of the logic lines goes low below thisaforementioned generated voltage, the EEPROM would be reversed biasedwhich could damage the part. Separating the heater and EEPROM groundseliminates all these possibilities for damage to the EEPROM.Accordingly, it is desirable to electrically isolate the heateraltogether from the other elements of the electrical circuit. Thus, asper FIG. 9, a first electrical pad (electrical pad 5, for example) ofthe plurality of electrical pads is connected only to a first terminalend of the heater trace, while a second electrical pad (electrical pad6, for example) of the plurality of electrical pads is connected only tothe second terminal end of the heater trace.

With reference to FIG. 8B, presume that the thermal sensors are NTC(negative temperature coefficient) thermistors. In this case, the commonsignal on electrical pad 2 is held at a constant voltage level toprovide Vcc for the EEPROM and a reference voltage for the thermistors.Control is switched via the thermistor/EEPROM switch circuit betweenreading the thermistors and clocking/reading/writing the EEPROM. TheTable of Signals and Electrical Characteristics summarizes an exemplaryconstruction of the interface 785.

Table of Signals and Electrical Characteristics Element Signals andElectrical Characteristics Thermal sensors Common reference signal is3.3 volts DC. Outputs 740, 742 are analog. Heater 726 Total resistance6.5 to 7.0 ohms driven by a pulse width modulated waveform of 3.3 voltsDC. The power density of the peripheral portion 729 is 30%-60% higherthan that of the center portion 728. EEPROM 770 Ground is 0 volts. Vccis 3.3 volts DC. SCL and (Micron SDA pins see a low impedance sourceswitched Technology in parallel with the thermistor outputs.24AA01T-I/OT)

In a best mode of practice, a temperature measurement device accordingto FIG. 8A has been fabricated using the materials and parts listed inthe following table. An electrical circuit with copper traces and padswas formed on a flexible substrate of polyimide film by a conventionalphoto-etching technique and thermal sensors were mounted using aconventional surface mount technique. The dimensions in the table arethicknesses, except that signifies diameter. Of course, these materialsand dimensions are only illustrative and in no way limit the scope ofthis specification. For example, the traces may be made wholly or partlywith electrically conductive ink. In another example, the thermalsensors are preferably thermistors, but PN junctions, thermocouples, orresistance temperature detectors can also be used.

Table of Materials and Parts: II Representative dimensions/ ElementMaterial/Part characteristics Flexible 2 mil thick Polyethylene tere-Substrate 701: substrate phthalate (PET) film with depos- 0.05 mm thick701, heater ited and photo-etched ½ oz. 726, contacts, copper traces andpads and and pads immersion silver-plated contacts. Thermal NegativeTemperature Coefficient 10k thermistors sensors (NTC) thermistors, Part# R603- in 0603 package. 740, 742 103F-3435-C, Redfish Sensors. FlexibleClosed cell polyethylene foam with Insulator 702: insulating skinnedmajor surfaces coated with {acute over (Ø)}40 × 3.0 mm thick layerspressure sensitive adhesive (PSA) Insulator 709: 702, 709 {acute over(Ø)}40 × 3.0 mm thick Stiffener 10 mil thick PET film Stiffener: 0.25 mmthick EEPROM Micron Technology 24AA01T- 770 I/OT

In a second construction of the measurement device 700, illustrated inFIG. 10, the heater 726 includes central and peripheral heater portions728 and 729 with different power densities, but the electrical circuitdoes not include a multi-pin electronic circuit device. In thisconstruction five electrical pads are provided on the tab 708. Absenceof the electronic circuit device permits deletion of at least oneelectrical pad from the tab, which further reduces the size and mass ofthe tab, and the cost of manufacturing the measurement device. Onlyelectrical pad 2 is shared: it provides a common reference signal forthe first and second thermal sensors.

In a third construction of the measurement device 700, illustrated inFIG. 11, the heater 726 includes central and peripheral heater portions728 and 729 with different power densities, and the electrical circuitdoes not include a multi-pin electronic circuit device. In thisconstruction four electrical pads are provided on the tab. Absence ofthe electronic circuit device permits deletion of at least oneelectrical pad from the tab. Further, electrical pad 3 is shared so asto provide a common reference signal for the first and second thermalsensors 740 and 742, and for the heater 726, permitting deletion ofanother electrical pad and further reduction in the size and mass of thetab 708, and the cost of manufacturing the measurement device.

In a fourth construction of the measurement device 700, illustrated inFIG. 12, the electronic circuit device 770 is included, but no slits areprovided in the substrate 701, and so the heater 726 includes continuouscentral and peripheral portions 728 and 729 with different powerdensities. Six electrical pads having the same connections as shown inFIGS. 8A and 8B are provided on the tab 708. In a fifth construction ofthe measurement device 700, illustrated in FIG. 13, the electroniccircuit device is not included, the heater 726 includes central andperipheral portions 728 and 729 with different power densities, and noslits are provided in the substrate 701. Five electrical pads having thesame connections as shown in FIG. 10 are provided on the tab 708. Thefifth construction can be further simplified to provide four electricalpads as per the third construction illustrated in FIG. 11 by sharing anelectrical pad so as to provide a common reference signal for the firstand second thermal sensors 740 and 742 and the heater. In the fourth andfifth constructions, the heater 726 is not penetrated by nonpowered slitareas; therefore, to maximize temperature uniformity, only the longaisle 780 need be powered.

In sixth and seventh constructions of the measurement device 700,illustrated in FIGS. 14 and 15, respectively, the heater trace 726includes three traces: a first trace 810 that defines the central heaterportion 728, a second trace 811, surrounding the first trace 810, thatdefines the peripheral heater portion 729, and a third trace 812connected to the first and second traces at a shared node 814. The thirdtrace 812 serves as a common connection between the first and secondtraces. This heater construction is thus constituted ofindependently-controlled central and peripheral heater portions thatshare a common lead. Alternatively, the construction can be consideredas a heater with two heater elements. The power densities of the centraland peripheral portions can be uniform or nonuniform. If the powerdensities of the two portions are uniform, the peripheral portion can bedriven at a higher power level than the central portion so as to providethe desired higher power density. As per FIGS. 8B, 9, 14, and 15 thesecond heater construction requires three separate pins (6, 7, and 5)for the first, second, and third traces. Thus, for a construction of theelectrical circuit that includes two independently-controlled heaterportions that share a common lead, and a memory device, seven electricalpads are provided on the tab 708. As with the first heater construction,the heaters of the second heater construction are entirely electricallyisolated from the other elements of the electrical circuit. In thisregard, with reference to FIGS. 9 and 14, the heater trace 726 includesthree terminal ends and a first electrical pad (electrical pad 5, forexample) of the plurality of electrical pads is connected only to afirst terminal end of the heater trace, a second electrical pad(electrical pad 6, for example) of the plurality of electrical pads isconnected only to the second terminal end of the heater trace, and athird electrical pad (electrical pad 7, for example) of the plurality ofelectrical pads is connected only to the third terminal end of theheater trace.

In an eighth construction of the measurement device 700 including aheater 726 with two heater elements as per FIG. 16, elimination of thememory device reduces the electrical pin count to six, if an electricalpad is shared to provide a common reference signal for the first andsecond thermal sensors; sharing an electrical pad so as to provide acommon reference signal for the thermal sensors and the heaters permitsthe electrical pad count to be reduced to five.

It is not necessary that the flexible substrate be configured with acircular central section, nor is it necessary that the annular heater begenerally circular. In ninth and tenth constructions of the measurementdevice 700, illustrated in FIGS. 17 and 18, respectively, the centralsubstrate sections have multilateral and oval (or elliptical) shapes, asdo the heaters. Each heater construction includes central and peripheralpower density portions and a nonpowered central zone surrounded by theheater. All of the constructions previously described can be adapted tothese shapes as required by design, operational, or manufacturingconsiderations.

Although principles of temperature measurement device construction andmanufacture have been described with reference to presently preferredembodiments, it should be understood that various modifications can bemade without departing from the spirit of the described principles.Accordingly, the principles are limited only by the following claims.

The invention claimed is:
 1. A zero-heat-flux temperature device withfirst and second flexible substrate layers sandwiching a layer ofthermally insulating material, in which a heater trace disposed on thefirst substrate layer defines a heater including a central power densityportion surrounding a zone of the first substrate layer having no heatertrace and a peripheral power density portion surrounding the centralpower density portion, a first thermal sensor is disposed in the zone, asecond thermal sensor is disposed on the second substrate layer, aplurality of connection pads is disposed outside of the heater trace,and a plurality of conductive traces connects the first and secondthermal sensors and the heater trace with the plurality of connectionpads.
 2. The zero-heat-flux temperature device of claim 1, in which theflexible substrate includes a center section, a tab extending outwardlyfrom the periphery of the center section, and a tail extending outwardlyfrom the periphery of the center section, the plurality of connectionpads is disposed on the tab, and the center section and the tail arefolded around the layer of thermal insulating material such that thecenter section constitutes the first substrate layer and the tailconstitutes the second substrate layer.
 3. The zero-heat-fluxtemperature device of claim 2, in which the central power densityportion has a first power density and the peripheral power densityportion has a second power density that is greater than the first powerdensity.
 4. The zero-heat-flux temperature device of claim 3, in whichthe central power density portion has an annular shape and theperipheral power density portion has an annular shape that is concentricwith the central power density portion annular shape.
 5. Thezero-heat-flux temperature device of claim 3, further comprising apattern of slits in the center section extending from the periphery ofthe center section toward the zone, in which the heater trace includesportions flanking the slits with a power density that is greater thanthe first power density.
 6. The zero-heat-flux temperature device ofclaim 3, further comprising a bulbous enlargement at the end of the tailin which the second thermal sensor is disposed.
 7. The zero-heat-fluxtemperature device of claim 3, in which the heater trace includes twoterminal ends and a first connection pad of the plurality of connectionpads is connected only to a first terminal end of the heater trace and asecond connection pad of the plurality of connection pads is connectedonly to the second terminal end of the heater trace.
 8. Thezero-heat-flux temperature device of claim 2, in which the centersection has a substantially circular shape and the tail and tab areseparated by an arc of less than or equal to 1800 on the periphery ofthe center section.
 9. The zero-heat-flux temperature device of claim 8,in which the plurality of connection pads includes at least fourconnection pads.
 10. The zero-heat-flux temperature device of claim 9,in which the tab includes opposing notches.
 11. The zero-heat-fluxtemperature device of claim 1, in which the central power densityportion includes a first heater trace portion, the peripheral powerdensity portion includes a second heater trace portion separate from thefirst heater trace portion, and the heater trace further includes acommon heater trace portion separate from the first and second heatertrace portions and connected at a shared node to the first and secondheater trace portions.
 12. The zero-heat-flux temperature device ofclaim 11, in which the central power density portion has an annularshape and the peripheral power density portion has an annular shape thatis concentric with the central power density portion annular shape. 13.The zero-heat-flux temperature device of claim 12, further comprising apattern of slits in the center section extending from the periphery ofthe center section toward the zone, in which the second heater traceportion includes elongate portions flanking the slits.
 14. Thezero-heat-flux temperature device of claim 11, in which the heater traceincludes three terminal ends and a first connection pad of the pluralityof connection pads is connected only to a first terminal end of theheater trace, a second connection pad of the plurality of connectionpads is connected only to the second terminal end of the heater trace,and a third connection pad of the plurality of connection pads isconnected only to the third terminal end of the heater trace.
 15. Thezero-heat-flux temperature device of claim 1, further comprising apattern of slits in the center section extending from the periphery ofthe center section toward the zone in which the heater trace includeselongate portions flanking the slits.
 16. A temperature device,comprising: a flexible substrate; and, an electrical circuit on theflexible substrate, the electrical circuit including an annular heatertrace surrounding a zone of the flexible substrate, a first thermalsensor disposed in the zone, a second thermal sensor disposed outside ofthe annular heater trace, a multi-pin electronic circuit device, aplurality of connection pads disposed outside of the annular heatertrace, and a plurality of conductive traces connecting the first andsecond thermal sensors, the multi-pin electronic circuit device, and theheater trace with the plurality of connection pads.
 17. The temperaturedevice of claim 16, in which the annular heater trace includes a centralheater portion having a first power density and a peripheral heaterportion having a second power density that is greater than the firstpower density.
 18. The temperature device of claim 17, in which theplurality of connection pads includes six connection pads.
 19. Thetemperature device of claim 18, in which the multi-pin electroniccircuit device is a programmable memory device.
 20. The temperaturedevice of claim 16, in which the annular heater trace includes a centralheater portion including a first heater trace portion, a peripheralheater portion including a second heater trace portion separate from thefirst trace portion, and a common heater trace portion separate from thefirst and second heater trace portions and connected at a shared node tothe first and second heater trace portions.
 21. The temperature deviceof claim 20, in which the plurality of connection pads includes sevenconnection pads.
 22. The temperature device of claim 21, in which themulti-pin electronic circuit device is a programmable memory device.